[Objective] To investigate the non-additive effect of different maize straw components on soil organic carbon (SOC) mineralization in loessial soil in order to provide technical support for soil CO₂ emissions.[Methods] By laboratory incubation experiment, five treatments were set including soil with no maize straw addition (CK); soil with stalk litter addition (CKS); soil with leaf litter addition (CKL); soil with leaf sheath addition (CKLS) soil with mixed maize straw addition (CKM).[Results] The amounts of observed soil accumulative carbon mineralization were significant higher than the predicted value in the end of experiment, and the promotion was mainly happened in the fast decomposition stage (1~28 d). The predicted remaining mass and carbon-nitrogen ratio were higher than the observed values, while the predicted content of soil total nitrogen was lower than the observed value in the end of experiment. The content of microbial biomass carbon (MBC) was the highest under CKS treatment, and there was no significant difference among other treatments. The content of microbial biomass nitrogen (MBN) showed a decreasing tendency, the MBC/MBN increased under litter addition treatments and the differences among CKS, CKL and CKM treatments and CK treatment was significant. The content of dissolved organic carbon (DOC) was higher under CKLS and CKM treatments than under other three treatments, and the difference between CKS and CKL treatments was not significant.[Conclusion] To mix litter in proportion had a synergistic effect on litter decomposition, and the decomposition of mixed litter promoted litter nitrogen accumulation.